let a:string="zs"
let b:number=12
const c:boolean=false
let d:any =23
d =true
let e:unknown= 56
if(typeof e==="number"){
    console.log(e.toFixed(2))
}
let f:null=null
let g:undefined=undefined

function add():void{
    console.log("23")
}
function add1():never{
     console.log("23")
     throw new Error("出错了")
}
